2000 Chevy Silverado Knocking

It is probably carbon build-up on the piston skirts. Get 2 cans of GM top engine cleaner liquid at your local dealer. On a cold engine, remove the spark plugs, unplug the ignition coils, pour 1/4 can of cleaner into each spark plug hole. Don't worry if you overfill the hole. Be sure not to get it on paint. Let the vehicle sit overnight with the cleaner in the cylinders. Then, cover the fenders and engine with a drop cloth or something. Crank the engine over to blow out all of the cleaner. You will notice all of the carbon deposits come out too. Put the spark plugs back in, change the oil and filter, and start the engine. It will smoke really bad for a couple of miles, but you should notice the knock is now gone.